Recent increases in petroleum prices have led to the development of "drier" fuels for engines used in heavy equipment and vehicles, such as earth-moving equipment, trucking, locomotives, and farm machinery. Drier fuels usually include methane, which tends to be corrosive to, and produce greater heat in the engines. These fuels, in turn, have led to spark ignited engines, which are more efficient at running on the drier fuels. Manufacturers of the spark ignited engines recommend regular maintenance checks, such as every 750 hours of operation.
An important part of the maintenance check includes checking the exhaust valves for a "tulip condition". A tulip condition is characterized by a bulge or concavity in the head of an engine valve, which causes the valve stem to extend upwardly from the engine head more than normal. The tulip condition is usually caused by excessive heat from the dry fuels used in the engine, which breaks the grain lines in the metal and deforms it.
One recommended way to check for a tulip condition is to periodically measure the exhaust valve stem height to determine if it has changed since the last maintenance check. There are usually two exhaust valves per cylinder, and four to sixteen cylinders per engine. The valve stem height is measured when the engine is new, to establish a baseline measurement, and then that baseline height is compared to the measured height at future maintenance checks. In the past, valve stem heights were measured after taking the engine apart, including the rocker box. This was a time-consuming and expensive procedure. The valve stem height has also been measured with a depth micrometer extending from a bar placed across the top of the rocker box, to save disassembly costs. But if the rocker box was ever removed or disturbed in the future, as it frequently is during maintenance, the baseline measurement would no longer be valid and could not be validly compared to future valve stem height measurements. Also, the rocker box has a compressible gasket which could affect each measurement due to inconsistent compression. Thus, there is a need for an inexpensive and reliable way to measure exhaust valve stem height.